Sea urchins or urchins are small, spiny, globular creatures that compose part of class Echinoidea. They're found in oceans all over the world. Their shell, or "test",'s round and spiny, typically from 3 to 10 cm across. Common colors include black and dull shades of green, olive, brown, purple, and red. They move slowly, feeding mostly on algae. Sea otters, wolf eels, and other predators feed on urchins. Sea urchins are also harvested by humans and their roe's served as a delicacy. Sea urchins… (More on Echinoidea)